This invention relates a process for the manufacture of trans-1,3,3,3-tetrafluoropropene (HFO trans-1234ze). More particularly, the invention pertains to a process for the manufacture of the HFO trans-1234ze by first dehydrofluorinating 1,1,1,3,3-pentafluoropropane to thereby produce a mixture of cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride. Then optionally recovering hydrogen fluoride, followed by recovering trans-1,3,3,3-tetrafluoropropene.
Traditionally, chlorofluorocarbons (CFCs) like trichlorofluoromethane and dichlorodifluoromethane have been used as refrigerants, blowing agents and diluents for gaseous sterilization. In recent years, there has been widespread concern that certain chlorofluorocarbons might be detrimental to the Earth's ozone layer. As a result, there is a worldwide effort to use halocarbons which contain fewer or no chlorine substituents. Accordingly, the production of hydrofluorocarbons, or compounds containing only carbon, hydrogen and fluorine, has been the subject of increasing interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids. In this regard, trans-1,3,3,3-tetrafluoropropene (trans-1234ze) is a compound that has the potential to be used as a zero Ozone Depletion Potential (ODP) and a low Global Warming Potential (GWP) refrigerant, blowing agent, aerosol propellant, solvent, etc, and also as a fluorinated monomer.
It is known in the art to produce HFO-1234ze (i.e. HydroFluoroOlefin-1234ze). For example, U.S. Pat. No. 5,710,352 teaches the fluorination of 1,1,1,3,3-pentachloropropane (HCC-240fa) to form HCFC-1233zd and a small amount of HFO-1234ze. U.S. Pat. No. 5,895,825 teaches the fluorination of HCFC-1233zd to form HFC-1234ze. U.S. Pat. No. 6,472,573 also teaches the fluorination of HCFC-1233zd to form HFO-1234ze. U.S. Pat. No. 6,124,510 teaches the formation of cis and trans isomers of HFO-1234ze by the dehydrofluorination of HFC-245fa in the presence of an oxygen-containing gas using either a strong base or a chromium-based catalyst. European patent EP 0939071 describes the formation of HFC-245fa via the fluorination of HCC-240fa through intermediate reaction product which is an azeotropic mixture of HCFC-1233zd and HFO-1234ze.
It has been determined that these known processes are not economical relative to their product yield. It has also been noted that significant amount of cis-1234ze is generated together with its trans-isomer in these know processes. Hence, there is a need for means by which trans-1234ze can be isolated from product mixtures and cis-1234ze can be recycled. Accordingly, the present invention provides an integrated process for producing trans-1234ze from which highly pure trans-1234ze can be obtained at a higher yield than prior art processes and cis-1234ze can be recycled in contrast to known processes. In particular, it has now been found that trans-1234ze may be formed by dehydrofluorinating 1,1,1,3,3-pentafluoropropane in the absence of an oxygen-containing gas to produce a mixture of cis-1,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene and hydrogen fluoride. Then optionally, but preferably recovering hydrogen fluoride and then recovering trans-1,3,3,3-tetrafluoropropene. The cis-1234ze and HFC-245fa may then be recycled.